Sender Policy Framework, or SPF, is a verification system, which is employed to prevent the so-called e-mail spoofing where an e-mail message is sent from one address, but to seem as being sent from another one, generally with the purpose to fraud the recipient in some way. When SPF protection is activated for a domain name, a specific record is made for it in the Domain Name System and all of the DNS servers globally get it. The record includes all mail servers that are allowed to send legitimate messages from an e-mail address under the domain. When a message is sent, the very first DNS server it encounters checks the SPF record and in case the sending server is permitted, the message is forwarded to the target receiver. When, however, the sending server is not contained in the SPF record for the particular domain, the email message will not be submitted and it'll be discarded. In case you employ this solution, it'll prevent third parties from sending spam emails which look as if they have been sent from you.